The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems including UNIX and Windows NT. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards.
Apache has been the most popular web server on the Internet since April 1996.
Roxen WebServer is a full-featured open-source web server distributed under the GPL license. It runs on a number of different operating systems including Windows, Linux, Solaris and Mac OS X.
Some of the strong points of this server is:
Savant is a freeware open source web server that runs on Windows 9x, ME, NT, 2000, and XP turning any desktop computer into a powerful web server. Designed to be fast, secure, and efficient, Savant is the choice of thousands of professional and amateur webmasters worldwide.